Thermosetting solid propellant composition comprising nonvolatile tertiary amine and method for controlling cure rate of the composition

ABSTRACT

Disclosed are a nitrate ester polyether-based thermosetting solid propellant composition comprising a nonvolatile tertiary amine, and a method for controlling a viscosity buildup of the nitrate ester polyether-based thermosetting solid propellant composition characterized by adding a nonvolatile tertiary amine.

TECHNICAL FIELD

The present invention relates to a thermosetting solid propellant composition comprising a nonvolatile tertiary amine, and a method for controlling a cure rate of the composition.

BACKGROUND ART

Solid propellant is produced by homogenously mixing its all ingredients, casting in a preset frame during the time, for which the fluidity of the propellant is maintained to allow the casting process (hereinafter, referred to as “pot life”, and curing at the temperature of 50 to 60° C. for 7 to 10 days.

In a nitrate ester polyether (NEPE)-based minimum smoke propellant, a nitramine oxidizing agent, for example, 1,3,5-trinitroperhydro-1,3,5-triazine (RDX), 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX), 2,4,6,7,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (HNIW) or the like, is used, and thus, its variation exponent of a combustion rate depending on a pressure change (i.e., pressure exponent) is very high, namely, at least 0.6. Accordingly, in order to reduce the pressure exponent, a ballistic modifier, such as lead or bismuth compounds, has been used in propellant formulation.

Since metallic ions or acidic substances having effects on a curing reaction can be dissolved in the NEPE-based propellant formulated with a polar binder system, some of bismuth or lead compounds used as a ballistic modifier may be dissolved in raw materials of the propellant during mixing process of the propellant. In this case, a large amount of bismuth ion and acid, which act as a catalyst in the propellant curing reaction, are generated in the propellant composition, so as to excessively promote the propellant curing reaction, which makes the viscosity of the propellant be drastically increased after the completion of the mixing process, not allowing sufficient time to cast the propellant. That is, the time for which the fluidity of the propellant is maintained (i.e., the pot life) may not be appropriately secured.

The curing reaction rate depends on temperature as well as a cure catalyst. Thus, where the curing reaction is promoted by any cure catalyst components, in the conventional method, the mixing and casting processes of the propellant should be conducted at a lower temperature, such as below 15° C., which is lower than the typical processing temperature of 50° C. in order to reduce the curing reaction rate. However, in order to maintain such a low temperature, a refrigerating equipment is required, thereby increasing a preparation cost, which is a problem to be necessarily solved.

DISCLOSURE OF INVENTION Solution to Problem

Therefore, an object of the present invention is to provide a method for increasing the time, for which the fluidity of a propellant is maintained, by controlling a viscosity buildup of a nitrate ester polyether (NEPE)-based solid propellant composition.

Another object of the present invention is to provide a method for preparing a nitrate ester polyether (NEPE)-based solid propellant composition, enabling to carry out mixing and casting processes at room temperature, at which cooling with tap water is possible without any separate refrigerating system.

The objects of the present invention can be achieved by the followings:

(1) A nitrate ester polyether-based thermosetting sold propellant composition, comprising 1 to 4% by weight of bismuth subsalicylate as a ballistic modifier, and 0.005 to 0.03% by weight of a nonvolatile tertiary amine as a cure rate modifier, with respect to the total weight of the composition.

(2) A method for controlling a viscosity buildup of a nitrate ester polyether-based thermosetting sold propellant composition comprising bismuth subsalicylate as a ballistic modifier, characterized by adding to the composition 0.005 to 0.03% by weight of a nonvolatile tertiary amine selected from the group consisting of 1.4-diazabicyclo[2.2.2]octane, 1,5-diazabicyclo[4.3.0]non-5-ene, 1,8-diazabicyclo[5.4.0]undec-7-ene and any combination thereof.

The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.

Advantageous Effects of Invention

In accordance with the present invention, the nonvolatile tertiary amine is used as a cure rate modifier, thereby preventing from drastic viscosity buildup, which is caused due to a bismuth compound used as a ballistic modifier acting as a curing reaction catalyst, which makes it possible to maintain the viscosity as low as enabling to carry out mixing and casting processes of the propellant at room temperature.

In the present invention, mixing and casting processes of the propellant can be conducted at room temperature, and the temperature can be maintained at room temperature using tap water as a coolant, whereby any separate refrigerating system is not required.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.

In the drawings:

FIG. 1 shows viscosity buildup curves for a propellant depending on temperature (a: 15° C., b: 25° C., c: 50° C.);

FIG. 2 shows viscosity buildup curves for propellants with or without addition of DABCO at 25° C. (a: with DABCO, b: without DABCO);

FIG. 3 shows viscosity buildup curves for propellants depending on the kinds of tertiary amine at 25° C. (a: addition of 0.013% by weight of DABCO, b: addition of 0.015% by weight of DBU, c: addition of 0.02% by weight of DBN); and

FIG. 4 shows viscosity buildup curves for propellants depending on the content of DABCO at 25° C. (a: addition of 0.003% by weight, b: addition of 0.013% by weight, c: addition of 0.02% by weight).

MODE FOR THE INVENTION

Description will now be given in detail of the preferred embodiments according to the present invention, with reference to the accompanying drawings.

The present invention relates to a nitrate ester polyether (NEPE)-based thermosetting solid propellant composition comprising bismuth subsalicylate as a ballistic modifier and a nonvolatile tertiary amine as a cure rate modifier.

It has been known that the curing reaction rate of the thermosetting solid propellant composition is influenced mainly by temperature, a cure catalyst and acidity.

In the NEPE-based minimum smoke propellant, a lead or bismuth compound is used as a ballistic modifier. Especially, bismuth subsalicylate, unlike lead compounds, is environmentally friendly and is very superior in improving combustion characteristics.

However, bismuth subsalicylate has been well known to have a very strong catalytic function in a urethane curing reaction and to promote the urethane curing reaction in an acidic condition. Bismuth subsalicylate causes generation of acids when it is mixed with a nitrate ester plasticizer and a polar polymer. Thus, when the propellant composition is mixed at 50° C. which is a typical processing temperature, it is cured so fast to lead to a drastic increase of viscosity, which results in shortening of the pot life.

In order to overcome such problems, in the conventional method, mixing and casting of the propellant have been conducted at a temperature of below 15° C., thereby lowering the viscosity buildup of the propellant and extending the port life (See U.S Pat. No. 6,168,677). The method of this patent, however, is undesirable because it requires a refrigerating system for maintaining the temperature at 15° C.

The present invention was completed based on the recognition that the cure rate of the propellant can be controlled if acids generated during the propellant mixing process are neutralized with an appropriate base, and in this case, the mixing and casting processes can be carried out at a higher temperature than that in the conventional art.

Many substances may be used to neutralize acids. However, in the present invention, an inorganic base, or a primary or secondary organic amine cannot be used because they may cause a urethane reaction or aging of the propellant. A volatile base also cannot be used because the propellant mixing process is conducted under a vacuum condition. Therefore, in the present invention, a nonvolatile tertiary amine, which does not cause any urethane reaction or aging of the propellant, and is nonvolatile under a vacuum condition, is used as a base for neutralizing acids generated during the mixing process of the propellant composition.

The nonvolatile tertiary amine is selected from the group consisting of 1.4-diazabicyclo[2.2.2]octane (hereinafter, referred to as “DABCO”, 1,5-diazabicyclo[4.3.0]non-5-ene (hereinafter, referred to as “DBN”, 1,8-diazabicyclo[5.4.0]undec-7-ene (hereinafter, referred to as “DBU”, and any combination thereof, and the content of the nonvolatile tertiary amine is preferable to have 0.005 to 0.03% by weight with respect to the total weight of the thermosetting solid propellant composition. If the amount of the tertiary amine is less than 0.005% by weight, an appropriate pot life is not secured, and if the amount of the tertiary amine exceeds 0.03% by weight, a curing reaction is not normally proceeded.

The thermosetting solid propellant composition according to the present invention may have the same composition as a typical NEPE-based minimum smoke propellant composition, except for comprising a ballistic modifier and further comprising a nonvolatile tertiary amine as a cure rate modifier. Therefore, in addition to the nonvolatile tertiary amine, the propellant composition of the present invention may comprise 20 to 30% by weight of a nitrate ester plasticizer, 55 to 62% by weight of a nitramine oxidizing agent, 1 to 1.5% by weight of a combustion stabilizer, 1 to 4.0% by weight of a ballistic modifier, 0.5 to 2.0% by weight of a stabilizer, and polymers (prepolymers and curing agent) composing the rest.

The nitrate ester plasticizer may be selected from the group consisting of nitroglycerin, butanetriol trinitrate, trimethylolethane trinitrate, triethylene glycol dinitrate, diethylene glycol dinitrate, n-butyl nitratoethylnitramine, and any combination thereof, and the polymer may be selected from the group consisting of polyethylene glycol, glycidyl azide polymer, polydiethylene glycol adipate, ORP-2, poly caprolactone, and any combination thereof.

Preferably, the ballistic modifier is bismuth subsalicylate.

In the present invention, the addition of a small amount of the nonvolatile tertiary amine allows neutralization of acids generated during the mixing process of the NEPE-based minimum smoke propellant, by which the curing reaction rate of the propellant is controlled, thereby enabling to sufficiently extend the time of maintaining the pot life of the propellant composition even at room temperature, i.e., at the temperature range of 20 to 25° C. Since the present invention enables to carry out the mixing and casting processes of the propellant at room temperature, tap water can be used as a coolant.

Therefore, the present invention relates to a method for controlling a viscosity buildup of a nitrate ester polyether (NEPE)-based thermosetting solid propellant composition comprising bismuth subsalicylate as ballistic modifier, by addition of a non-volatile tertiary amine to the composition.

The present invention also relates to a method for preparing a nitrate ester polyether (NEPE)-based thermosetting solid propellant composition, characterized by adding a nonvolatile tertiary amine during a mixing process for preparing the propellant composition, and conducting mixing and casting processes at room temperature.

EXAMPLES

Hereinafter, a detailed description will be given in accordance with examples of the present invention. However, the examples are merely illustrative, and should not be construed as limiting the scope of the present invention to the range of the examples.

Comparative Example

2% by weight of bismuth subsalicylate as a ballistic modifier was added to a mixture of 5.9% by weight of polyethylene glycol, 1.2% by weight of 1,3,5-tris(6-isocyanatohexyl)-1,3,5-triazine-2,4,6-trione (N-3200) as a curing agent, 22.2% by weight of butanetriol trinitrate, 7.0% by weight of trimethylolethane trinitrate, 30% by weight of HNIW and 29% by weight of RDX as nitramine oxidizing agents, 0.8% by weight of N-methyl para-nitroaniline (NMA), 0.2% by weight of acrylonitrile-2-hydroxyethyl acrylate copolymer as a neutral polymeric binding agent, and 1.3% by weight of zirconium carbide and 0.4% by weight of carbon black as additives.

Thereafter the viscosity buildup of the composition depending on time and temperature was observed. The observation results are shown in FIG. 1, wherein lines a, b and c indicate viscosity buildup curves at 15° C., 25° C. and 50° C., respectively.

After completion of the propellant mixing, in order for the propellant to be smoothly cast in a preset mold, the viscosity of the propellant should be below about 20 kilopoise. Line a in FIG. 1 shows that the viscosity of the propellant composition of the comparative example is maintained below 10 kilopoise at 15° C. for at least 6 hours, line b in FIG. 1 shows that the viscosity of the propellant composition of the comparative example exceeds 20 kilopoise at 25° C. in 2 hours, and line c in FIG. 1 shows that the fluidity of the propellant composition of the comparative example disappeared to the extent that casting become impossible at 50° C. in 10 minutes. Therefore, it was concluded that the composition of the comparative example allows casting of the propellant at 15° C. but not at a temperature higher than 15° C.

Example 1

The same propellant composition as that in the comparative example was prepared, except that 0.013% by weight of DABCO, with respect to the total weight of the composition, was further added at the time when the curing agent was added. The viscosity buildup of the composition depending on time at 25° C. was observed. The observation results are shown in line a in FIG. 2. Line b in FIG. 2 is the viscosity buildup curve of the composition according to the comparative example at 25° C. which is included in FIG. 1 for the comparison with Example 1 of the present invention. Line a in FIG. 2 shows that the viscosity buildup of the composition of Example 1 of the present invention at 25° C. is similar to that of the comparative example at 15° C., which means that the viscosity buildup of the composition according to Example 1 of the present invention at 25° C. is much lower than that of the composition according to the comparative example at 25° C. as shown in line b in FIG. 2. Therefore, it can be understood that the mixing and casting processes can be carried out with the composition according to Example 1 of the present invention at 25° C.

Example 2

The same propellant composition as that in Example 1 was prepared, except that 27% by weight of HMX were used as a nitramine oxidizing agent instead of 30% by weight of HNIW, and 3% by weight of polymers was additionally used. The viscosity change depending on time at 25° C. was observed. The similar viscosity buildup pattern to line a in FIG. 2 was observed.

In order to maintain the processing temperature for preparing the propellant at 15° C., a refrigerating system is required to maintain the temperature of a coolant below 15° C., whereas the temperature of 25° C. can be maintained only using tap water as a coolant.

The reason why the curing reaction rate can be controlled by the addition of a small amount of DABCO in Examples 1 and 2 is that acids generated from bismuth subsalicylate are neutralized by DABCO.

Example 3

In case that DBN or DBU, instead of DABCO, was used, similar results to those in Examples 1 and 2 were observed.

FIG. 3 shows the comparison of the viscosity buildup of the compositions at 25° C. according to examples of the present invention. Line a in FIG. 3 shows results when 0.013% by weight of DABCO was added, line b in FIG. 3 shows results when 0.015% by weight of DBU was added, and line c in FIG. 3 shows results when 0.02% by weight of DBN was added. FIG. 3 shows that the addition of each of the three tertiary amines results in a similar viscosity buildup pattern to one another.

FIG. 4 shows the variation of the propellant viscosity depending on the contents of DABCO and time. Line a in FIG. 4 shows results when 0.003% by weight of DABCO was added, line b in FIG. 4 show results when 0.013% by weight of DABCO was added, and line c in FIG. 4 shows results when 0.02% by weight of DABCO was added. Line a in FIG. 4 shows a drastic viscosity buildup after four hours, whereas line c in FIG. 4 shows that almost no viscosity change was observed for up to 8 hours. For line c in FIG. 4, after completion of the propellant cure, the hardness of the propellant was lower than that in a or b in FIG. 4, which is inferred because the curing reaction was not normally proceeded. Therefore, it was concluded that the optimum content of DABCO is 0.013% by weight of the total composition.

Such results indicate that since the nonvolatile tertiary amine has no volatility and reactivity, it has no effect on other characteristics of the propellant. Therefore, it was found that the nonvolatile tertiary amine is a useful additive when preparing a propellant composition.

The foregoing embodiments and advantages are merely exemplary and are not to be construed as limiting the present disclosure. The present teachings can be readily applied to other types of apparatuses. This description is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art. The features, structures, methods, and other characteristics of the exemplary embodiments described herein may be combined in various ways to obtain additional and/or alternative exemplary embodiments.

As the present features may be embodied in several forms without departing from the characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its scope as defined in the appended claims, and therefore all changes and modifications that fall within the metes and bounds of the claims, or equivalents of such metes and bounds are therefore intended to be embraced by the appended claims. 

1. A nitrate ester polyether-based thermosetting solid propellant composition, comprising, with respect to the total weight of the composition, 1 to 4% by weight of bismuth subsalicylate as ballistic modifier, and 0.005 to 0.03% by weight of a nonvolatile tertiary amine as a cure rate modifier.
 2. The composition according to claim 1, wherein the nonvolatile tertiary amine is selected from the group consisting of 1.4-diazabicyclo[2.2.2]octane, 1,5-diazabicyclo[4.3.0]non-5-ene, 1,8-diazabicyclo[5.4.0]undec-7-ene and any combination thereof.
 3. A method for controlling a viscosity buildup of a nitrate ester polyether-based thermosetting solid propellant composition comprising bismuth subsalicylate as a ballistic modifier, characterized by adding 0.005 to 0.03% by weight, with respect to the total weight of the composition, of nonvolatile tertiary amine selected from the group consisting of 1.4-diazabicyclo[2.2.2]octane, 1,5-diazabicyclo[4.3.0]non-5-ene, 1,8-diazabicyclo[5.4.0]undec-7-ene and any combination thereof. 